Imaging periodic currents using alternating balanced steady-state free precession
Imaging periodic currents using alternating balanced steady-state free precession
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DOI：
10.1002/mrm.21457
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发表时间：
2008-01-01
影响因子：
3.3
通讯作者：
Wong, Eric C.
中科院分区：
文献类型：
--
作者：
Buracas, Giedrius T.;Liu, Thomas T.;Wong, Eric C.
现有的功能性脑MR成像方法仅通过替代信号（诸如脑实质的血管床中的脱氧血红蛋白浓度）间接地检测神经元活动。最近有人提出，神经元电流可以直接使用MRI（ncMRI）测量。然而，在使用标准梯度或自旋回波脉冲序列的神经元电流检测研究中报告了有限的成功。平衡稳态自由进动（bSSFP）脉冲序列的独特之处在于它可以提供最高的信噪比效率，并且对自由进动相位的扰动非常敏感。本文报道，当自旋相位扰动周期性电流被锁定到RF脉冲串时，相位扰动在多个RF激励上累积，并且自旋磁化达到有效地放大由于电流引起的相位扰动的交替平衡稳态（ABSS）。因此，ABSS信号的交替对弱周期性电流高度敏感。当前采用ABSS成像的体模实验在持续36秒的扫描中检测到小至0.15nT的磁场变化，这比使用梯度回忆回波成像更灵敏。Magn Reson Med 59：140-148，2008. (C)2007 Wiley-Liss，Inc.
Existing functional brain MR imaging methods detect neuronal activity only indirectly via a surrogate signal such as deoxyhemoglobin concentration in the vascular bed of cerebral parenchyma. It has been recently proposed that neuronal currents may be measurable directly using MRI (ncMRI). However, limited success has been reported in neuronal current detection studies that used standard gradient or spin echo pulse sequences. The balanced steady-state free precession (bSSFP) pulse sequence is unique in that it can afford the highest known SNR efficiency and is exquisitely sensitive to perturbations in free precession phase. It is reported herein that when a spin phase-perturbing periodic current is locked to an RF pulse train, phase perturbations are accumulated across multiple RF excitations and the spin magnetization reaches an alternating balanced steady state (ABSS) that effectively amplifies the phase perturbations due to the current. The alternation of the ABSS signal therefore is highly sensitive to weak periodic currents. Current phantom experiments employing ABSS imaging resulted in detection of magnetic field variations as small as 0.15nT in scans lasting for 36 sec, which is more sensitive than using gradient-recalled echo imaging. Magn Reson Med 59: 140-148, 2008. (C) 2007 Wiley-Liss, Inc.